Various designs exist for dental bone conduction hearing aid systems that use radio transmission of external ambient sound from an extra-oral device to an intra-oral device. Such devices function as receivers of radio frequency-modulated (FM) or amplitude-modulated (AM) transmission. For example, see U.S. Pat. No. 2,995,633 to Puharich; U.S. Pat. No. 5,447,489 to Issalene; U.S. Pat. No. 5,033,999 to Mersky; and U.S. Pat. No. 5,460,593 to Mersky.
Many devices rely on a “send mode” of transmitting non-acoustic signals recorded in the bone conduction pathway or through the body. For example, U.S. Pat. No. 6,823,195 to Boesen discloses ear microphones. U.S. Pat. No. 6,047,163 to Miyoshi discloses a miniature loop antenna placed on the wrist with the two antenna leads capacitively-coupled through the body. Other references describe tooth microphones from a first unit worn inside the mouth to a radio receiver second unit worn outside the mouth. For example, see U.S. Pat. No. 7,269,266 to Anjannappa. U.S. Patent Publication No. 2009/0022351 to Wieland et al. describe an inductive mode of “send” transmission of speech data from a tooth device having only a single receiving antenna, which responds to changes in the magnetic field created by movement of a magnet attached to a tooth. U.S. Pat. No. 6,394,969 to Lenhardt relates to a tinnitus suppressor and masker. U.S. Patent Publication No. 2009/0270673 to Abolfathi et al. relates to methods and systems for tinnitus treatment comprising an oral appliance having an electronic and/or transducer assembly for generating sounds via a vibrating transducer element. U.S. Patent Publication No. 2007/0280495 to Abolfathi et al. discloses methods and apparatus for processing audio signals. U.S. Pat. No. 5,447,489 to Issalene et al. relates to a hearing aid device comprising an extra-buccal wireless transmitter part and an intra-buccal wireless receiver transducer part for receiving signals from the transmitter part and comprising at least one vibrating element. U.S. Patent Publication No. 2009/0281433 to Saadat et al. relates to systems and methods for determining a pulmonary function by mounting one or more sensors intra-orally, capturing intra-oral data, and determining the pulmonary function based on an analysis of the intra-oral data. U.S. Patent Publication No. 2009/0274325 to Abolfathi relates to methods and apparatus for transmitting vibrations via an electronic and/or transducer assembly through a dental patch. U.S. Pat. No. 7,153,257 to Schneider et al. relates to an implantable hearing aid system that includes a transducer housing that is rotatable relative to a transducer mounting apparatus to orient the transducer for interfacing with an auditory component. Other devices transmit vibrations via an electronic and/or actuator assembly through a dental appliance.
Typically in dental bone conduction hearing aid systems, one antenna is located in the mouth, while the other external antenna is placed somewhere on the body. Conventional hearing aid systems are prone to decreasing and/or inefficient antenna placement and signal transmission, and inconsistent signal strength and clarity. In particular, if antennas are not optimally aligned, the power necessary for the signal transmission is overdone, and thus precious battery power is wasted. As a result, ease of use and efficiency of such conventional systems is degraded.
In conventional hearing aid systems, a variety of obstacles have thwarted the use of low-power radio and inductive signal transmissions to and from the human mouth. One such obstacle is the variability in the skull size, skull mass, and dentition. Further, the electrical charge of human skin and tissue creates interference to an internally disposed (in-mouth) antenna. Moreover, determining or measuring in-situ the actual strength of a low-power electromagnetic signal transmission to and from the mouth poses a technological challenge. In addition, slight movements of either the transmitting or receiving antenna during usage typically results in signal noise or degradation, thereby degrading optimal positioning of the antennas.
Thus, there is a need to establish a stable and repeatable co-location of an antenna of an extra-oral device relative to an antenna of an intra-oral device.